The debate on whether to keep or sacrifice the posterior cruciate ligament (hereinafter sometimes referred to as “PCL”) has existed in the orthopedic community for several years, and is likely to remain for several more. Cruciate retaining (hereinafter sometimes referred to as “CR”) knee implants allow for retention of the PCL, while posterior stabilizing (hereinafter sometimes referred to as “PS”) knee implants typically feature a mechanism between the femoral component and tibial insert to reproduce femoral rollback and stabilize the knee joint.
Conventional CR and PS designs have their pros and cons. On one hand, CR users typically argue that keeping the PCL helps stability, promotes femoral rollback, and reduces forces transmitted to the bone-implant interface, because the PCL absorbs some of those forces. In addition, CR femoral components typically do not require additional bone cut from the intercondylar area of the femur, making them typically more bone-preservation friendly than PS components. On the other hand, PS users typically argue that removing the PCL helps correct any preexisting deformities, reduces polyethylene (PE) wear, and offers more potential congruency between femoral and tibial components.
It is believed that the knee market (as of 2008) was relatively well balanced between PS and CR knee implants (see FIG. 1—Worldwide knee market segmentation between CR and PS knee implants in 2002 and 2008—2008: 49% PS, 51% CR; 2002: 43% PS, 57% CR).
A CR knee system is typically intended for patients who, in the physician's judgment, have good bone stock and whose ligaments provide adequate mediolateral, anteroposterior, and varus/valgus stability. The PCL is expected to be healthy to help stability and the kinematics of the knee joint (see FIG. 2—Front and back views of the right knee). However, there is a risk the PCL will lose function later and become deficient, which could lead to the need for revision due to instability and pain. In revision cases, the surgeon typically has no other choice than to sacrifice the PCL, remove both the CR femoral component and CR tibial insert, and implant a PS femoral component and PS tibial insert. This type of revision is typically associated with femoral bone loss due to removal of the well-fixed femoral component, and may be particularly harmful to the patient. Because of this risk, some CR-oriented surgeons have been switching to PS implants. The knee market segmentation between CR and PS shown in FIG. 1 illustrates this trend from 2002 to 2008.
Various patents related to prosthetic knees include the following:
U.S. Pat. No. 6,629,999, entitled MODULAR JOINT, which was issued Oct. 7, 2003 in the name of Serafin, Jr.
U.S. Pat. No. 5,405,398, entitled PROSTHETIC KNEE WITH POSTERIOR STABILIZED FEMORAL COMPONENT, which was issued Apr. 11, 1995 in the name of Buford, III, et al.
U.S. Pat. No. 5,116,375, entitled KNEE PROSTHESIS, which was issued May 26, 1992 in the name of Hoffmann.
U.S. Pat. No. 4,309,778, entitled NEW JERSEY MENISCAL BEARING KNEE REPLACEMENT, which was issued Jan. 12, 1982 in the name of Buechel et al.
Among those benefits and improvements that have been disclosed, other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying figures. The figures constitute a part of this specification and include illustrative embodiments of the present invention and illustrate various objects and features thereof.